The present invention relates to a multi-stage sorting means or apparatus for sorting a mixture of solid materials into lightweight and heavy materials, the mixtures comprising lumpy, granular and pulverous constituents of differing specific gravity, such as mixtures of coal and mine waste, or ore and refined ore.
In a sorting device of this kind, differences in density between the solid components of a dry mixture are used for the purpose of separation. In the case of conventional box-like means for dry sorting, the entire sorting means is vibrated during operation and an adjustable pulsating air flow is introduced into the processing chamber in order to produce a fluidized bed. During the process, particles having lower specific gravity are raised by the pulsating air flow and enter an overflow as a result of vibration, whereas the denser particles collect at the bottom on a screen. For various reasons, separation attainable by these means is still unsatisfactory. For example, a clean separation cannot be obtained if the difference in density between the components that are to be separated is relatively slight. Frequently such sorting devices are difficult to operate unless they are continuously supplied with material for processing. Box-like sorting devices also take up a relatively large amount of space.
It is therefore an object of the present invention to provide a sorting means that can cleanly separate lighter from heavier material even when the differences in density between the particles to be separated are slight; furthermore, the sorting means should be very reliable, simple to operate, and economic in use. In addition, the sorting means should be compact.